Changes in heat stabilizers and in printing inks over the years has resulted in a loss of printability of flexible poly (vinyl chloride) substrates. The curtailment of heavy metals (e.g. cadmium) in stabilizers and of volatile solvents in both stabilizers and printing inks has been held responsible for the loss of printability. Thus, there has arisen a need for a way to enhance the wettability of such present day PVC substrates.
A patent application by Witco Corporation published under the number WO96/15186 teaches that the wettability of heat-stabilized PVC film to water-based inks and the adherence of such inks to the film are improved by the incorporation of oxidized polyethylene in the PVC composition. The heat stabilizer is a mixture of barium and zinc carboxylates having up to 20 carbon atoms in combination with organic phosphites.
The surface tension of a heavy metal-containing PVC has been found to be from 25 to 33% higher than that of a traditionally plasticized PVC according to E. R. Napoleon in “Journal of Vinyl & Additive Technology”, 3, No. 2, 145 (June 1997).
As taught in co-pending, commonly assigned patent application Ser. No. 09/133,605, filed Aug. 13, 1998, the teachings of which are incorporated herein by reference, the degradation products of a blocked or latent mercaptan present during processing of the halogen-containing resin at an elevated temperature enhance the activity of metal-based heat stabilizers such as organotin carboxylates and mercaptides in the composition. Vinyl chloride resin compositions and articles made thereof are stabilized particularly well by a combination of very low levels of zinc carboxylates and latent mercaptans selected from the group consisting of 2-S-(hydroxyalkylthio)-tetrahydropyran, 5-S-(hydroxyalkylthio)tetrahydrofuran, 6-S-(2formylhydroxyalkylthio)tetrahydropyran, the carboxylic acid esters of said alcohols, and mixtures of said alcohols and esters. Said latent mercaptans are also referred to as 2-S-(tetrahydropyranyl)-thioalkanol; 2-S-(tetrahydropyranyl)thioalkyl carboxylate; 6-S-(2-formyl-tetrahydropyranyl)thioalkanol and carboxylates thereof, and their furanyl homologs, i.e., 5-S-(tetrahydrofuranyl)thioalkanol, and 5-S-(tetrahydrofuranyl)-thioalkyl carboxylate.